Stearic acid desaturase gene negatively regulates the thermotolerance of Pinellia ternata by modifying the saturated levels of fatty acids

Pinellia ternata is an important medicinal plant; in particular, its tuber has broad medical applications. However, thermal stress limits the commercial production of this plant, and the mechanism by which P. ternata plants respond to heat stress has not been unraveled. In the present study, a stearic acid desaturase gene (PtSAD) that is involved in thermal stress response was functionally characterized. PtSAD accumulated predominantly in aboveground tissues (>4-fold) and was remarkably induced by heat stress but not by drought, cold, and salt. The overexpression of PtSAD decreased the thermotolerance of P. ternata and increased the proportion of unsaturated fatty acids. By contrast, gene knock-out conferred increased thermotolerance and significantly elevated the proportion of saturated fatty acids. Compared with wild-type plants, three CRISPR/Cas9 lines performed better while overexpression transgenics performed worse with respect to biomass, net photosynthesis (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 content (Ci), electrolyte leakage (El) and reactive oxygen species (ROS) under heat stress. These results showed that PtSAD functions as a negative regulator in the thermal response in P. ternata, and its knockout is a potential bioengineering strategy to overcome the negative effects of heat in the summer.